/* 
 * Kodkod -- Copyright (c) 2005-2007, Emina Torlak
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */
package kodkod.ast;


import kodkod.ast.visitor.ReturnVisitor;
import kodkod.ast.visitor.VoidVisitor;


/**
 * An expression whose value depends on the truth of a given condition.
 * 
 * @specfield condition: Formula
 * @specfield thenExpr: Expression
 * @specfield elseExpr: Expression
 * @invariant children = 0->condition + 1->thenExpr + 2->elseExpr
 * @author Greg Dennis (gdennis@mit.edu)
 * @author Emina Torlak
 */
public final class IfExpression extends Expression {

	private final Formula condition;
	private final Expression thenExpr, elseExpr;
	private final int arity;
	
	/**
	 * @effects this.condition' = condition && this.thenExpr' = thenExpr &&
	 *         this.elseExpr' = elseExpr
	 * @throws IllegalArgumentException - thenExpr.arity != elseExpr.arity
	 */
	IfExpression(Formula condition, Expression thenExpr, Expression elseExpr) {
		if (thenExpr.arity() != elseExpr.arity()) {
            throw new IllegalArgumentException("Arity mismatch: " +
            		thenExpr + "::" + thenExpr.arity() +  " and " +
            		elseExpr + "::" + elseExpr.arity());
        }
		this.condition = condition;
		this.thenExpr = thenExpr;
		this.elseExpr = elseExpr;
		this.arity  = thenExpr.arity();
	}
	
	/**
	 * Returns the if-condition.
	 * @return this.condition
	 */
	public Formula condition() {
		return condition;
	}
	
	/**
	 * Returns the then-expression.
	 * @return this.thenExpr
	 */
	public Expression thenExpr() {
		return thenExpr;
	}

	/**
	 * Returns the else-expression.
	 * @return this.elseExpr
	 */
	public Expression elseExpr() {
		return elseExpr;
	}
	
	/**
	 * Returns the arity of this.
	 * @return this.arity
	 */
	@Override
	public int arity() {
		return arity;
	}

	/**
	 * {@inheritDoc}
	 * @see kodkod.ast.Expression#accept(kodkod.ast.visitor.ReturnVisitor)
	 */
	public <E, F, D, I> E accept(ReturnVisitor<E, F, D, I> visitor) {
		return visitor.visit(this);
	}

	/**
	 * {@inheritDoc}
	 * @see kodkod.ast.Node#accept(kodkod.ast.visitor.VoidVisitor)
	 */
	public void accept(VoidVisitor visitor) {
		visitor.visit(this);
	}

	/**
	 * {@inheritDoc}
	 * @see kodkod.ast.Node#toString()
	 */	public String toString() {
		return "(if " + condition + " then " + thenExpr + " else " + elseExpr + ")";
	}
	
}
